The invention relates to tactile output devices for blind persons displaying symbols and graphics provided by a computer. The invention also relates to input devices for blind computer users.
Known tactile displays employ electromagnetically or piezoelectrically driven pins to provide the information to the tactile perception of the user. An electromagnetic display element is described by Alfred Bottig in his German Pat. No. 1,094,808, issued Dec. 15, 1960. Tactile devices provide up to 80 braille symbols or 144 dots of graphic information (Kay, L. Electronic aids for blind persons; an interdisciplinary subject. In: IEE Proceedings, Vol. 131, Pt.A. No. 7, September 1984, S.559,576). Another approach is to stimulate the skin of the user by limited electrical current (Brummer. Hans: Untersuchung von elektrotaktilen Schrift- und Bildtasverfaren fur Blinde. By: VDI Verlag, Eusseldorf, Germany, 1987). Braille printers can be used to display symbolic and graphic information on special paper.
In some cases it would be advantage to provide a whole drawing or a variable portion of a drawing to the user. Examples of this are: reading usual block print books containing text and drawings making use of a scanner or a camera, reading a map using an information system, and creating drawings by means of a computer. With braille printers the user has to produce a copy before deciding if the information is useful and will further have to produce a copy after each modification or zooming of the drawing. Electromagnetic and piezoelectric display elements are expensive, especially if they are bistable to provide a storage of their states. Additionally, these elements can be packed in graphically useful distances of about 0.05 inch only with great effort. Electrotactile methods are not well liked by its users, and driving a large amount of electrodes separately is very expensive as is true with all elements without bistable states.
Electrorheological fluids are fluids that raise their viscosity reversibly if an electrical field is applied. Additionally they adhere to the electrodes and the volume of the fluid increases under the influence of the field. An electrorheological fluid is described by Willis M. Winslow in his U.S. Pat. No. 2,417,850 issued Mar. 25, 1947: U.S. Pat. No. 2,661,596, issued Dec. 8, 1953; and U.S. Pat. No. 3,047,507, issued Jul. 31, 1962. A valve for electrorheological fluids is described by John W. Mark and Howard H. Barney in their U.S. Pat. No. 3,587,613, issued Jun. 28, 1971. A pump using electrorheological fluids is described in the Soviet Pat. App. No. 2,481,802/06.